JP2001218471A - Switching power supply - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide a simple configuration, prevent inrush current, and prevent starting failure of a converter. SOLUTION: The present invention provides a rectifier 5 which rectifies AC power into DC power, is connected to an output terminal of the rectifier 5, and smoothes a pulsating flow of DC power from the rectifier 5; It has an inrush current prevention circuit 6 connected in series with the capacitor C to prevent inrush current, and a series connection of the inrush current prevention circuit 6 and the smoothing capacitor C is connected in parallel with the converter 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching power supply, and more particularly to a switching power supply that has a simple configuration and prevents inrush current.

[0002]

2. Description of the Related Art As a conventional switching power supply, as disclosed in Japanese Patent Application Laid-Open No. 10-97327,
It has an inrush current prevention circuit provided between the rectifier and the switching circuit, and this inrush current prevention circuit is composed of a negative characteristic thermistor or a series circuit of a positive characteristic thermistor and a resistor connected in parallel with the negative characteristic thermistor and a resistor. There is a known device that prevents inrush current. FIG. 4 is an electric circuit diagram showing a conventional switching power supply device described in Japanese Patent Application Laid-Open No. 10-97327. As shown in FIG. 4, the switching power supply device 65 includes AC voltage input terminals 51a and 51a.
1b, fuse 52, choke coils 53a, 53b,
It comprises a rush current prevention circuit 62 comprising a capacitor 54, a rectifier 55, and a negative characteristic thermistor 56, an electrolytic capacitor 57 constituting a smoothing capacitor, and output terminals 58a and 58b. A switching circuit (not shown) is connected to the output terminals 58a and 58b. The rectifier 55 has input terminals 55a and 55b and output terminals 55c and 55d.

The AC power input to the AC voltage input terminals 51a and 51b (for example, AC 100V, frequency 50H)
z) is a fuse 52, choke coils 53a, 53
b, input terminal 55 of rectifier 55 via capacitor 54
a, 55b. The AC power supplied to the input terminals 55a and 55b is rectified by the rectifier 55, and is converted into pulsating DC power including a DC component and a ripple component between the output terminals 5c and 5d. Output terminals 55c, 55 of rectifier 55
The DC power of d is limited in current by an inrush current prevention circuit 62 comprising a negative characteristic thermistor 56, and an electrolytic capacitor 57
And supplied to the switching circuit (not shown) from the output terminals 58a and 58b. When the power supply of the switching power supply (circuit) 65 is turned on, the negative characteristic thermistor 56 constituting the inrush current prevention circuit 62 is turned on.
Is not charged, the electrolytic capacitor 57 is not charged.
Is limited by an integrating circuit composed of a resistor of the negative characteristic thermistor 56 and an electrolytic capacitor 57.
Further, the negative characteristic thermistor 56 has a characteristic that the resistance value decreases when the temperature rises. Therefore, the resistance value is such that the inrush current is sufficiently limited at normal temperature. The voltage loss in the resistance of the pulsating voltage generated between the terminals 55c and 55d is suppressed small,
The output terminals 58a and 58b are configured to supply sufficient power to a switching circuit (not shown). However, the switching power supply device 65 includes the inrush current prevention circuit 6.
2 is composed of the negative characteristic thermistor 56, and when the power supply of the switching power supply 65 is turned on in a state where the ambient temperature is sufficiently lower than the normal temperature, the resistance value of the negative characteristic thermistor 56 is large. However, the voltage drop of the pulsating voltage generated between the output terminals 55c and 55d due to the high resistance becomes large, so that a sufficient power cannot be supplied to the switching circuit, and there is a problem that the starting failure of the switching circuit occurs. . In order to eliminate such a starting failure of the switching circuit, the inrush current prevention circuit 62 has been improved.

FIG. 5 is an electric circuit diagram showing another switching power supply device disclosed in Japanese Patent Application Laid-Open No. 10-97327. As shown in FIG. 5, in the switching power supply device 50, only the inrush current prevention circuit 61 is different from the switching power supply device 65 shown in FIG.
Only 1 will be described. The inrush current prevention circuit 61 is configured by a circuit in which a positive characteristic thermistor 59 and a resistor 60 are connected in series, and a negative characteristic thermistor 56 is connected in parallel to the serially connected circuit. The resistance value of the resistor 60 is set to a value that can sufficiently suppress the rush current, and the positive characteristic thermistor 59 is used.
Is set to be substantially the same as the resistance value of the resistor 60 at normal temperature, the resistance value is sufficiently small at low temperature, and sufficiently large at high temperature. Further, the negative characteristic thermistor 56 has a value slightly larger than the resistance value of the resistor 60 at room temperature,
The resistance is set to be sufficiently large at a low temperature and sufficiently small at a high temperature. In this manner, the combined resistance value of the inrush current prevention circuit 61 is low when the resistor 6
The resistance is set to be sufficiently smaller than the resistance of the resistor 60 at a high temperature, substantially the same as the resistance of 0. This allows
When the ambient temperature is low, the inrush current prevention circuit 61 can prevent the inrush current since the combined resistance value is almost the same as the resistance value of the resistor 60 even when the power is turned on. Can be done. Also,
When the temperature of the negative characteristic thermistor 56 rises, the combined resistance value becomes sufficiently smaller than the resistance value of the resistor 60, and sufficient power can be supplied to the switching circuit.

[0005]

In the conventional switching power supply device 50, start-up failure at low temperature can be eliminated, but the positive characteristic thermistor 59, the resistor 60 and the negative characteristic thermistor 56 are required. As the number of circuit components increases, the component cost of the positive temperature coefficient thermistor 59 and the negative temperature coefficient thermistor 56 is high, and there is a problem that the cost of the device is increased. An object of the present invention is to solve such problems. That is, an object of the present invention is to provide a switching power supply device that has a simple configuration, can prevent an inrush current, and can prevent a starting failure of a converter.

[0006]

According to a first aspect of the present invention, there is provided a rectifier connected to an output terminal of the rectifier, the rectifier being connected to an output terminal of the rectifier. A smoothing capacitor for smoothing the pulsating flow of the DC power, and an inrush current prevention circuit connected in series with the smoothing capacitor to prevent inrush current, wherein a series connection of the inrush current prevention circuit and the smoothing capacitor is provided. It is characterized in that it is connected in parallel with the converter. According to a second aspect of the present invention, in the first aspect of the present invention, the inrush current prevention circuit includes a negative characteristic thermistor. According to a third aspect of the present invention, in the switching power supply device according to the first aspect, the inrush current prevention circuit includes a resistor. According to a fourth aspect of the present invention, in any one of the first to third aspects,
The switching power supply device according to (1), further comprising a discharge diode connected in parallel with the inrush current prevention circuit so as to be in a forward direction with respect to the discharge of the smoothing capacitor.

[0007]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. 1 is an electric circuit diagram showing a switching power supply device according to one embodiment of the present invention. In FIG. 1, a switching power supply 1 includes a rectifier configured by input terminals 2a and 2b that receive AC power from an AC power supply (for example, a frequency of 50 Hz and 100V), a fuse 3, choke coils 4a and 4b, a capacitor C1, and a diode bridge. , A rush current prevention circuit 6, a smoothing capacitor C, a discharging diode D, and a converter 7. 5a and 5b are AC input terminals of the rectifier 5, 5c and 5d are rectification output terminals of the rectifier 5, and 7a and 7b are input terminals of the converter 7. The fuse 3 is applied to the input terminals 2a and 2b with a large voltage generated by a surge (for example, a lightning surge) exceeding a use voltage of an assumed AC power supply (for example, a commercial power supply having a frequency of 50 Hz and 100V), and a large current flows. In case the circuit breaks. Further, the fuse 3 has a short circuit in the circuits subsequent to the fuse 3 (for example, a short circuit between the terminals 5a and 5b, a short circuit between the terminals 5c and 5d, and the terminals 7a and 7b
Circuit, etc.). The choke coils 4a and 4b and the capacitor C1 constitute a low-pass filter (LPF), which removes high-frequency noise and the like superimposed on the AC power supply and supplies AC power to the AC input terminal 5.
a, 5b. The rectifier 5 forms a bridge with four diodes, performs full-wave rectification on the AC power applied to the AC input terminals 5a and 5b, and outputs a DC component and a ripple component (the frequency of the AC power 50Hz
In this case, a pulsating DC power of 100 Hz is output. The rectifier 5 always generates a positive (+) polarity voltage of the pulsating voltage on the rectification output terminal 5c side, and generates a negative (-) polarity voltage on the rectification output terminal 5d. One end of the inrush current prevention circuit 6 is a flat d-smoothing capacitor C.
And the other end is connected to the rectification output terminal 5c side. On the other hand, the negative (-) side of the smoothing capacitor C is connected to the rectification output terminal 5d side. Note that the rectified output terminal 5c and the input terminal 7a of the converter 7,
Since the rectified output terminal 5d and the input terminal 7b of the converter 7 are connected in a short-circuit state, the series connection circuit of the inrush current prevention circuit 6 and the smoothing capacitor C is connected in parallel with the converter 7.

The inrush current prevention circuit 6 is constituted by a negative thermistor or a resistor. When the power of the switching power supply 1 is turned on and the smoothing capacitor C is not charged, the inrush current prevention circuit 6 is supplied from the rectification output terminals 5c and 5d. The inrush current flowing into the smoothing capacitor C having a pulsating current is limited by the resistance of a negative characteristic thermistor or a resistor. If the rush current prevention circuit 6 is not provided, the pulsating current supplied from the rectification output terminals 5c and 5d instantaneously tries to charge the smoothing capacitor C and the rush current (impulse current) flows into the smoothing capacitor C. The capacitor C may be damaged. By connecting the inrush current prevention circuit 6 of the negative characteristic thermistor or the resistor and the smoothing capacitor C in series, an RC integrating circuit of the resistor and the capacitor can be formed. It becomes a value obtained by dividing the pulsating voltage by the resistance value, and thereafter decreases exponentially with a time constant determined by the capacitance and the resistance value of the smoothing capacitor C. Since the inrush current prevention circuit 6 is connected in series with the smoothing capacitor C and the connected body is connected in parallel with the converter 7, a resistor is provided between the rectification output terminals 5c and 5d and the input terminals 7a and 7b of the converter 7. Since there is no current limiting element such as a converter, the output of the rectifier 5 can be directly supplied to the converter 7, so that starting failure of the converter 7 does not occur and power loss is small.

Since the inrush current prevention circuit 6 is constituted by the negative characteristic thermistor RT shown in FIG. 2, by setting the resistance value of the negative characteristic thermistor RT high when the power supply of the switching power supply 1 is turned on, the smoothing capacitor C Inrush current to the power supply can be prevented. Next, as time elapses, the temperature of the negative characteristic thermistor RT rises due to the ripple component of the rectified pulsating flow, and the resistance value decreases, so that power loss to the converter can be reduced. Further, the inrush current prevention circuit 6 may be constituted by a resistor R as shown in FIG. 3, and in this case, it is possible to eliminate the trouble of selecting and managing the temperature characteristics. Also, a discharging diode D
Is connected in parallel with the inrush current prevention circuit 6 so as to be in the forward direction with respect to the discharge of the smoothing capacitor C. When the ripple component of the pulsating voltage output from the rectifier 5 is lower than the charging voltage value of the smoothing capacitor C, Can supply power from the smoothing capacitor C to the converter 7 via the discharging diode D. Therefore, even if the ripple component of the pulsating voltage fluctuates, stable power charged in the smoothing capacitor C can be supplied to the converter 7. Converter 7 is
Based on the stable power supplied from the input terminals 7a and 7b, the power is converted into high-frequency power, rectified and smoothed, and then a desired switching voltage is generated. The present invention is not limited to a commercial power supply having a wave number of 50 Hz and a voltage of 100 V, but can be applied to an AC power supply having a different frequency and voltage.

[0010]

As described above, according to the first aspect of the present invention, an inrush current is prevented by being connected in series with a smoothing capacitor connected to an output terminal of a rectifier and smoothing a pulsating flow of DC power from the rectifier. Since the inrush current prevention circuit is connected, and the series connection of the inrush current prevention circuit and the smoothing capacitor is connected in parallel with the converter, the inrush current can be prevented with a simple configuration, and The starting failure of the converter can be prevented, and the price can be reduced. Further, according to the first aspect of the present invention, since a current limiting element such as a resistor is not connected in series between the rectifier and the converter, power loss can be reduced. Further, the invention according to claim 2 is the same as the invention according to claim 1.
In the invention described in (1), since the inrush current prevention circuit is formed of a negative characteristic thermistor, the power loss can be further reduced in addition to the effect of the invention described in (1).
According to a third aspect of the present invention, in the first aspect of the present invention, the inrush current prevention circuit comprises a normal resistor. The trouble of selecting and managing the temperature characteristics of the characteristic thermistor can be eliminated. Further, the invention according to claim 4 is the invention according to any one of claims 1 to 3, further comprising a discharge diode D connected in parallel to the inrush current prevention circuit. Therefore, in addition to the effects of the invention described in any one of claims 1 to 3,
Stable power charged in the smoothing capacitor can be supplied to the converter.

[Brief description of the drawings]

FIG. 1 is an electric circuit diagram showing a switching power supply device according to one embodiment of the present invention.

FIG. 2 is an electric circuit diagram showing an inrush current prevention circuit of the switching power supply device of FIG.

FIG. 3 is an electric circuit diagram showing another inrush current prevention circuit of the switching power supply device of FIG. 1;

FIG. 4 is an electric circuit diagram showing a conventional switching power supply device.

FIG. 5 is an electric circuit diagram showing another conventional switching power supply device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Switching power supply device, 2a, 2b ... AC power input terminal, 3 ... Fuse, 4a, 4b ... Choke coil, C
1 ... capacitor, 5 ... rectifier, 5a, 5b ... input terminal,
5c, 5d: output terminal, 6: inrush current prevention circuit, C: smoothing capacitor, D: discharge diode, 7a, 7b: input terminal, 7: converter.

Claims (4)

[Claims] 1. A rectifier for rectifying AC power to DC power, a smoothing capacitor connected to an output terminal of the rectifier for smoothing a pulsating flow of DC power from the rectifier, and a rectifier connected in series with the smoothing capacitor. A switching power supply device comprising: an inrush current prevention circuit for preventing an inrush current; wherein a series connection of the inrush current prevention circuit and the smoothing capacitor is connected in parallel with a converter. 2. The switching power supply device according to claim 1, wherein said inrush current prevention circuit comprises a negative characteristic thermistor. 3. The switching power supply device according to claim 1, wherein said inrush current prevention circuit comprises a resistor. 4. The switching power supply according to claim 1, wherein the discharge is connected in parallel with the inrush current prevention circuit so as to be in a forward direction with the discharge of the smoothing capacitor. A switching power supply device, comprising: a switching diode.